What are Silicon Tuners?

What are Silicon Tuners?
Course Introduction
Purpose
• The intent of this course is to provide you with information about
Generation 2 MC44C801 and Generation 3 MC44S802 Silicon
Tuner products from Freescale Semiconductor.
Objectives
•
•
•
•
•
Define tuners and explain how they are used.
Differentiate between silicon tuners and CAN tuners.
List the advantages of silicon tuners over CAN tuners.
List applications for silicon tuners.
Calculate the output frequencies for single conversion and dual
conversion tuners.
• Describe the Generation 2 MC44C801 Silicon Tuner IC.
• Describe the Generation 3 MC44S802 Silicon Tuner IC.
Content
• 31 pages
• 5 questions
Learning Time
•
50 minutes
The Freescale Silicon Tuner Technical Training course covers both Generation
2 (Gen2) part number MC44C801 and Generation 3 (Gen3) part number
MC44S802 silicon tuner ICs from Freescale Semiconductor. This course begins
with an explanation of how tuners work and descriptions of CAN and silicon
tuners. It then examines the advantages of silicon tuners over CAN tuners.
Next, the MC44C801 and the MC44S802 are described. Finally, this course
looks at some of the advantages of using Freescale Silicon Tuners.
1
What are Silicon Tuners?
Definition:
• Tuners receive audio/video programming via a radio frequency (RF)
broadcast.
• Tuners select a single channel from the available channels on the
broadcast.
• Tuners convert RF signals into a lower, more workable frequency.
– RF to intermediate frequency (IF)
• Silicon tuners are highly integrated circuits that provide this
functionality in a single chip.
Competitive advantages:
• Have a lower overall system cost
• Have a smaller “footprint”
• Run through a standard factory flow
• Do not require manual tuning of coils
• Have a minimal power estimation calibration time
• Perform consistently and do not degrade over time
Tuners receive audio/video programming via an RF broadcast, then
select a single channel from the available channels on the broadcast.
The broadcast can be over-the-air (terrestrial), cable, or satellite. Next,
tuners convert the RF signals into a lower, more workable frequency.
Silicon tuners are highly integrated circuits that provide this functionality
in a single chip.
Let’s look at some of the advantages of silicon tuners. Ultimately, silicon
tuners enable a lower overall system cost. CAN tuners are still competing
today; however, they will soon run out of room for further price
reductions. In addition, silicon tuners have a much smaller footprint,
which allows you to use them in new, more portable applications.
During “end product” production, silicon tuners can run through a
standard factory flow, so no hand-soldering is required and they can go
though double-sided reflow. Silicon tuners do not require time-consuming
manual tuning of coils to provide image rejection. Power estimation
calibration time is minimal. For example, one customer reduced
calibration time from 2 minutes to 10 seconds using a Gen2 Silicon
Tuner. They meet DOCSIS power estimation specifications, and selfdiagnostics can further reduce test time.
Finally, silicon tuners reduce costs because they perform consistently;
there is little channel-to-channel variation in performance, and they do
not degrade over time.
2
Silicon Tuner Applications
•
•
•
Cable modems
Cable TV (CATV) set-top boxes (analog and digital)
CATV Media Gateway
– Cable modem + router
– Multi-room STB (Media Center)
•
•
•
•
•
Cable modem with integrated Voice-over-IP (VoIP)
Computer TV tuner cards (analog and digital)
Analog TV sets
Digital terrestrial TV sets
Digital terrestrial adapters
Here you can see some of the market applications for silicon tuners.
Gen2, which is the MC44C801, is best suited for digital
implementations such as the cable television, cable modems, cable
set-top boxes, media gateways, and cable modems with Voice over
IP (VoIP) functionality. Additionally, the MC44C801 can be used in
computer TV tuner cards because of their relaxed performance
specifications.
MC44S802, the Gen3 product, enables Freescale to target a
broader set of markets including analog TV, digital terrestrial TV,
digital terrestrial adapters, and all analog and digital cable-related
markets.
3
Broadband Frequency Spectrum
HBO
Food Network
FOX
Cartoon Network
15
dBmV
0
-15
100
200
300
500
400
600
700
800
900
MHz
I want to watch this channel,
not anything else. How do I
ignore the rest?
To better understand silicon tuners, let’s look at the background on RF
broadcasts and how they're handled.
In a broadband cable system, many channels are available to view.
In North America, each channel is 6 MHz wide spread across the 67 MHz to
860 MHz frequency range.
A tuner selects a single channel from the available channels. The tuner
must also be agile so that different channels can be selected as the user’s
preferences change.
Each channel carries useful information in it such as a series of pictures and
a sound track. A process called modulation encodes this information onto
the channel when the channel is created at the transmitter. The tuner in the
receiver must not damage the modulated signal so that the other parts of
the receiver can recover the useful information.
Several methods are used to select an individual channel from the mix, or
multiplex as it is called in the cable industry. All of these methods ultimately
result in filtering out the energy from the undesired channels, leaving only
the energy from the desired channel. The elements used to accomplish
filtering include devices that change a channels’ frequency (mixers),
amplifiers, and filters.
4
Legacy Single Conversion Tuner
UHF
Tuner AGC
SAW-filter
Mixer
Oscillator
Sound trap
(Ceramic)
Video
90°
VIF
LO
AGC
VHF(hi)
Antenna
FM
LO
demodulator.
38.9MHz
Sound
Sound filter
(Ceramic)
LO
Band
control
VHF(lo)
I2C-bus
Interface
÷P
LO
Vtune
÷N
SDA
SCL
÷R
PLL
Tracking filters,
manually aligned
Here you can see a more traditional tuner. This type of implementation is
still used today; however, silicon tuners are gradually replacing them.
The mixer oscillator array in the center of the diagram selects the
channel of interest.
Here you can see the array of filters with the antenna switch. This special
type of filter is called a tracking filter. With tracking filters, the pass band
can be changed as needed. However, tracking filter designs are limited
to a small range of frequencies, so three different filters are needed for
TV sets. As the channel is changed, the TV set selects and adjusts the
tracking filters.
Tracking filters also require adjustment at the time of manufacture. In the
past, a factory employee adjusted the coils to get the desired
performance. Even with today's manufacturing equipment, which
performs these adjustments with robotic tools, the adjustment of tracking
filters adds significant time to the manufacturing process. Finally, tracking
filter components have poor temperature and aging characteristics, so a
system that works when it rolls out the factory door will suffer degraded
performance as it ages and is exposed to temperature extremes.
Today, customers expect devices to work as soon as they come off the
manufacturing line and to continue to work for many years. Thus, we
need an approach to tuning channels that doesn't use tracking filters.
5
CAN Tuner
Manually Tuned Coils
Here we can see an example of a CAN tuner, which is a single conversion
tuner. They are called CAN tuners because they were put inside metal cans
for shielding purposes.
Note the presence of a hand-tuned coil in the tuner highlighted here. These
coils are part of the filtering system. In this tuner, the coil was tuned by
inserting a plastic screwdriver between the coil turns and expanding the coil
until the performance was within specification. This is a very labor-intensive
and time-consuming process. This particular design doesn't have a lot of
coils, but the designs used in most TV sets today have many more coils than
are visible in here.
6
Question
What are some of the advantages of using silicon tuners instead of CAN
tuners? Select all that apply and then click Done.
Lower overall system cost
Smaller footprint
Tracking filters improve performance
Perform consistently and do not degrade over time
Manually tuned coils allow for custom calibration
Done
What are some of the advantages of using silicon tuners?
Correct.
Silicon tuners have lower overall system cost, a smaller footprint, perform
consistently, and do not degrade over time. Manually tuned coils are a
characteristic of CAN tuners, and the process is time-consuming and laborintensive. Tracking filters, characteristic of legacy tuners, also require
manual adjustment and degrade over time.
7
RF Front End Basics
Mouse over each block to learn more about modern tuners.
Wideband
RF Input
LNA
Tuner
IF
Filter
IF
Amp
Demodulator
Low Noise Amplifier (LNA): The LNA adjusts the variations in power between channels and over
time.
Tuner: The tuner selects the frequency of interest, and the output is always at the same frequency.
The tuner selects the channel of interest from the input, filters out some of the other channels, and
converts the channel of interest to a fixed-frequency output.
IF: The tuner output is called the intermediate frequency (IF), and it contains the same modulated
information as was present at the input to the tuner. If the modulation is damaged by the tuner, the
information cannot be recovered.
Filter: The IF output of the tuner is further filtered to remove all the remaining undesired energy.
IF Amp: Most demodulators need the input power to be held within a small range, so an adjustable
amplifier is used between the tuner and the demodulator. Between the LNA and IF amplifier, the
system adjusts its gain with the power at the input to the demodulator centered within its operational
range as the power at the antenna input changes between channels and over time.
Demodulator: The last step in an RF front end is the input to the demodulator. The demodulator
and later blocks are responsible for recovering the modulated information from the IF.
Now let's take a look at the blocks in a modern tuner. Roll your mouse pointer
over each block for more information.
8
Mixer Math
Input Frequency: RF
Output Frequencies:
• RF
• LO
• RF+LO
• |RF-LO|
Input Frequency: Local
Oscillator (LO)
Now let's take a look at tuners in more detail. The mixer is the heart of the
tuner. Although the math is simple arithmetic, much can be done with a
mixer. The mixer generates two output signals from two input signals as
well as passing the input signal.
In the radio world, the input signals are commonly called RF and local
oscillator (LO). The LO signal is a clean sine wave, while the RF signal has
some form of modulation applied in order to carry information. The mixer
output contains the same modulation as the RF input, but at a new carrier
frequency as determined by the sum or difference of the RF and LO
frequencies.
The generated signals are the sum and difference of frequencies of the
input signal. In most tuners, only one of the output signals is used. The
modulation on the input signal is also passed through this mixer in the sum
and difference outputs.
9
Single Conversion Tuner
Input Frequency Range:
310-350 MHz
Low Pass Filter
Removes
RF+LO Energy
Desired Frequency:
320 MHz
Demodulator
40 MHz Input
Output Frequencies
Output Frequency (to be filtered)= RF + LO
600 MHz = 320 MHz + 280 MHz
Tunable PLL
270-310 MHz
Output Frequency (IF Input) = RF - LO
40 MHz = 320 MHz – 280 MHz
Set PLL to 280 MHz
Here is an example of mixer math at work. In this system, a high-frequency
RF signal input is reduced, or down converted, to a lower IF. The variablefrequency Phase Locked Loop (PLL) that generates the LO gives it the
ability to tune. As different channels are desired by the user, the PLL's
frequency is changed.
In this example, the desired frequency is 320 MHz, and the IF input to the
demodulator is 40 MHz. Thus, the PLL must be set to 280 MHz in order to
down convert the 320 MHz to 40 MHz. This example uses the difference
frequency. The 600 MHz output from the mixer, the sum component, may
need to be filtered before it reaches the demodulator, depending on the
design of the demodulator. This type of tuner is called a single conversion
down conversion because it's only using one mixer and because the input
frequency is reduced, or lowered, to a lower frequency. This type of tuner
was used in legacy TV sets.
Translating the input RF signal (320 MHz) to a lower frequency (40 MHz) is
called a down conversion. Using a PLL frequency (280 MHz) that is below
the input frequency (320 MHz) is called low side injection.
10
The Image Problem
Input Frequency Range:
310-350 MHz
Desired Frequency:
320 MHz
Undesired Energy:
240 MHz
Low Pass Filter
Removes
RF+LO Energy
Demodulator
40 MHz Input
Output Frequencies
Output Frequency (to be filtered) = RF +
LO 600 MHz = 320 MHz + 280 MHz
Output Frequency (IF Input) = |RF - LO|
Tunable PLL
40 MHz = |320 MHz – 280 MHz|
270-310 MHz
Set PLL to 280 MHz Output Frequency (IF Input) = |RF - LO|
40 MHz = |240MHz – 280 MHz|
Now consider what happens with the same system if energy is present
at 240 MHz. In this case, the difference product also results in a 40 MHz
output at the input to the demodulator. Both 240-MHz and 320-MHz
signals result in an IF of 40 MHz. If the energy is present at both
frequencies at the input, the IF output will be an incomprehensible mess
to the demodulator. The negative sign in the absolute value equation
indicates that a spectral inversion occurs.
11
Image: Another Perspective
LO
RF
Power
Image
Frequency
IF = RF - LO
IF = |Image - LO|
LO - Image = RF - LO
...or...
Image frequency = 2 x LO - RF
Another way to look at the problem of image is to look at a spectrum plot.
In this graph, the image frequency is the same distance from the LO as
the RF frequency. This also holds true with high-side injection. To
prevent the image energy from reaching the IF frequency, it must be
filtered before the mixer. Tracking filters are one method of removing the
image energy. However, as described earlier, they are undesirable in
modern electronics.
12
Dealing with a Poor Image
Input Frequency
Range: 310-350 MHz
Band
Pass
Filter
Low Pass Filter
Removes
LO+RF Energy
Desired Frequency:
320 MHz
Image: 240 MHz
Demodulator
40 MHz Input
Output Frequencies:
LO + RF = 600 MHz
|LO - RF| = 40 MHz
Tunable PLL
270-310 MHz
Set PLL to 280 MHz
Image energy must be filtered before the mixer, otherwise it cannot be
removed later. In this example, the band pass filter that allows 310 MHz
to 350 MHz would do the trick. However, in a real cable system, the
input frequency is much larger than the 40-MHz band shown in the
example. This means a series of tracking filters would be necessary and
they can be expensive and may perform unpredictably. If the image
frequency can be moved further from the desired RF band, the
requirements on the filter can be reduced. One way to move the image
frequency is by careful selection of the IF and LO frequencies. However,
this results in tighter constraints and higher costs in other parts of the
RF circuitry.
13
Image with Up Conversion
Mouse over the output frequency formulas to see the calculations.
Input Frequency
Range: 310-350 MHz
Low
Pass
Filter
Desired Frequency:
320 MHz
Image: 2320 MHz
Desired IF:
1000 MHz
Output Frequencies:
LO + RF = 1640 MHz
|LO – RF| = 1000 MHz
Output Frequencies
Tunable PLL
1050-1500 MHz
Set PLL to 1320 MHz
Output Frequency = LO + RF
1640 MHz = 1320 MHz + 320 MHz
Output Frequency = |LO – RF|
1000 MHz = |1320 MHz– 320 MHz|
One way to reduce the requirements on the image filter is to move the image
frequency far away from the desired frequency. This can be done by using an
up conversion in which the desired frequency is changed to a much higher
frequency. Because of the way the arithmetic works, the image frequency is
far away from the band of interest, so the filter can be a simple low pass filter
instead of a band pass or complex tracking filter array.
In this example, instead of converting the desired input of 320 MHz to an
output of 40 MHz, the IF is going to be up at 1 GHz. In this case, our PLL is
set to 1320 MHz, which means the difference frequency gives us our desired
IF. However, the IF is now at a very high frequency that is impractical or
probably even impossible to demodulate. So the requirements on the filter
have eased, but the requirements on the demodulator have increased. Roll
you mouse pointer over the output frequency formulas to see the calculations.
14
Question
Examine this single conversion tuner. What are the mixer output
frequencies? Select the correct answer and then click Done.
a. 616 MHz and 44 MHz
b. 330 MHz and 286 MHz
c. 374 MHz and 44 MHz
d. 616 MHz and 330 MHz
Low Pass
Filter
Removes
RF+LO Energy
Desired Frequency: 330 MHz
Demodulator
?? MHz Input
Tunable PLL
286 MHz
Consider this question regarding mixer math.
Correct.
The formulas for the output frequencies are output frequency = LO + RF and
output frequency = |LO – RF|. Therefore the two output frequencies are 616
MHz and 44 MHz.
15
Dual Conversion Tuner
Down Conversion
Up Conversion
Fixed
First IF
Tunable PLL
Fixed
Second IF
Band
Pass
Filter
Fixed PLL
•
First mixer up converts the signal to a frequency above the highest desired
signal in the input spectrum (first IF)
•
Image frequency = (2 x LO - RF)
•
Band pass filter removes the second IF image frequency
The dual conversion tuner provides an excellent method to deal with images
across a wide band of input frequencies. It provides the wide image
frequency separation shown with an up conversion mixer, while the following
down conversion mixer provides a suitable IF for the demodulator.
The first mixer up converts the signal to a frequency above the highest
desired signal in the input spectrum. The output of the first mixer is always
at a fixed frequency, called the first IF.
By using a first LO that is well above the highest frequency in the input to up
convert the RF, the image frequency is well above the input band. This
means the filter before the first mixer is not even needed in many cases.
Because the first IF and second IF are fixed, the image frequency for the
second mixer is also fixed. The band pass filter removes the second IF
image frequency.
The difficulty with this tuner is the first IF and first LO are at frequencies
above the highest frequency in the input band, which means the IF and LO
frequencies set the system performance requirement. CMOS processes
have been able to meet these requirements in a cost-effective manner for
broadband applications. With a dual conversion tuner, just as you saw in the
previous example with up conversion, the first IF output is at a high
frequency. The second mixer brings it back down to a frequency that can be
easily demodulated. This process greatly reduces the filter constraints on
the front end.
16
Tuning Cable Channels
First IF:
Desired:
80 MHz
1200 - 80 =1120 MHz
Band
Pass
Filter
Tunable PLL
1200 MHz
Second IF:
1120 – 1076 = 44 MHz
Output IF: 44 MHz
1076 MHz (fixed)
The math behind the dual conversion tuner is still simple arithmetic from the basic
mixer. However, because each mixer has image frequencies associated with it, the
number of arithmetic terms is much greater than in the single conversion mixer.
First we must define the channel of interest and the desired output frequency. We
will assume an input channel at 80 MHz and an output IF of 44 MHz. Further, we
must know the desired first IF of the system. With our tuner, the IF is 1120 MHz.
Now let's work through the forward-path math to determine the LO frequencies we'll
need for this configuration.
To up convert the input of 80 MHz to 1120 MHz, we'll use a first LO of 1200 MHz.
Remember, we're using the difference output from the mixer. This produces our first
IF of 1120 MHz.
Next this IF must be down converted to the desired output frequency of 44 MHz.
The second LO of 1076 MHz provides this result. Since the first IF is always 1120
MHz, the second LO does not change as the different input channels are tuned. All
tuning is accomplished by changing the first LO.
17
Tuning Cable Channels
Mouse over Image frequency = 2 x LO - RF to see the calculations
for the first and second IF image.
Desired:
80 MHz
First IF:
1200 - 80 =1120 MHz
Second IF Second IF:
1120 - 1076= 44 MHz
Image:
1032 MHz
Band
Pass
Filter
First IF Image:
2320 MHz
Tunable PLL
1200 MHz
1076 MHz (fixed)
Image frequency = 2 x LO – RF
First IF Image:
Second IF Image:
Image Frequency = 2 x LO – RF
Image Frequency = 2 x LO – RF
2320 MHz = 2 x 1200 MHz – 80 MHz
1032 MHz = 2 x 1076 MHz – 1120 MHz
Now let's consider what happens with the image frequencies in this system.
In a dual conversion tuner, there are two image frequencies: one for the first
mixer and one for the second mixer. The image frequencies are different
depending on the part of the system, and two image frequencies exist at the
input to the tuner.
Here you can see the formula for calculating the image frequency for the first
mixer. In this example, the result of this equation is 2320 MHz. Thus the
difference frequency, 1200 MHz minus 80 MHz equals 1120 MHz. The image
frequency for the first mixer also results in an output of 1120 MHz, since
2320 MHz minus the tuned LO of 1200 also results in 1120. In cable
systems, there is very little energy at this high frequency, so we actually don't
need a filter in front of the mixer.
The second mixer also has an image frequency. The same formula is now
used to tell us that the image frequency for the second mixer is at 1032 MHz.
Again, the absolute value of 1032 MHz minus the 1076 MHz for the LO of the
second mixer would result in an output of 44 MHz. Both the 1032 MHz and
the 1120 MHz input to the second mixer result in a 44MHz output. Roll your
mouse pointer over Image frequency = 2 x LO - RF to see the calculations
for the first and second IF image.
18
Tuning Cable Channels
Removes 2nd IF
image energy
Second IF Second IF:
1120 – 1076 = 44 MHz
Image:
1200 - 80 = 1120 MHz
1032 MHz
First IF:
Desired:
80 MHz
Band
Pass
Filter
First IF Image:
2320 MHz
Second IF Image:
168 MHz
Second IF Image:
|1032-1076| = 44 MHz
Tunable PLL
1200 MHz
1076 MHz (fixed)
Note:
Two mixers means two image frequencies at the input. The
second IF image is still inband but is now easily filtered by the
first IF filter.
Now let's take a look at how we can prevent energy at 1032 MHz from reaching the second mixer, and how we would
actually have energy present at 1032 MHz at the input to the second mixer. The only way for energy to reach the input
to the second mixer is from the output of the first mixer.
To have energy at 1032 MHz at the input to the second mixer, the first mixer must have up converted energy at its input
to 1032 MHz. By remembering that the output of any mixer is its RF minus LO, we can calculate the input frequency for
a desired output frequency as LO minus the mixer output. In this case, the first LO is 1200 MHz, so the result of 1200
MHz minus 1032 MHz is 168 MHz.
This means that without filters, energy at 168 MHz at the input to the first mixer will be up converted by the first mixer to
1032 MHz. Since 1032 MHz is the image frequency for the second mixer, the 168 MHz at the input to the tuner is an
image frequency for the second mixer. The advantage of the dual conversion tuner is that the second LO is fixed in
frequency, which means that its image frequency is also fixed. That's the 1032 MHz.
In a broadband system, energy is almost always present at 168 MHz because there are so many channels. It’s almost
guaranteed that the first up conversion will result in image energy at 1032 MHz. We must use a filter between the mixers
to remove that energy; otherwise, the resulting output IF will be unusable.
Another advantage of the dual conversion tuner is that the second LO is fixed in frequency, which means that its image
frequency is also fixed. Therefore, the filter to remove the image frequency is also a fixed-frequency device and tracking
filters aren’t necessary. The filter between the mixers accomplishes the work that was done by the tracking filters in the
single conversion tuner. The band pass filter only needs to be wide enough to pass the signals of interest.
One minor problem is that in the tuner, the first IF actually does move around a little bit. Due to the use of a 25 MHz
reference frequency, the first PLL tuning steps are made in 25 MHz steps. Since TV channels are spaced 6 MHz apart
in the U.S., the first IF is actually not always centered on 1120 MHz: the wide band is actually about 30 MHz. To account
for these small shifts in frequency, this tuner’s second LO is also tunable. The band pass filter must be wide enough to
account for the range of these possible first IFs (about 30 MHz).
With a dual conversion tuner, a wide range of input frequencies can be selected without the use of temperamental
manually tuned tracking filters. A single band pass filter between the mixers replaces the tracking filters used in the old
tuner designs. Today, the band pass filter is usually a surface acoustic wave (SAW) filter, which has performance
characteristics similar to those of modern semiconductors. The advent of advanced silicon processes that can support
the high first IF frequency enabled the creation of cost-effective dual conversion tuners.
19
Question
What are the roles of the two mixers in the dual conversion tuner? Select
the response that applies and click Done.
a.
The first is a down conversion mixer that provides wide image frequency
separation, while the second is an up conversion mixer that provides a
suitable IF for the demodulator.
b.
The first is an up conversion mixer that provides a suitable IF for the
demodulator, while the second is a down conversion mixer that provides
wide image frequency separation.
c.
The first is an up conversion mixer that provides wide image frequency
separation, while the second is a down conversion mixer that provides a
suitable IF for the demodulator.
Consider this question regarding the dual conversion tuner.
Correct.
The first mixer is for up conversion, and it provides wide image frequency
separation, while the second mixer is for down conversion, and it provides a
suitable IF for the demodulator.
20
Gain Control
Mouse over each amplifier to learn more.
LNA
Tuner IF
Control Signal
The RF LNA is often called a
front-end AGC amplifier.
The IF AGC is sometimes called
a back-end AGC amplifier.
IF AGC
Amp
Control Signal
RF Input
Power
Adjusted
Wideband
RF
Demodulator
IF Gain Control
RF Gain Control
Another aspect to consider is the gain control. The demodulator requires the power of
its input signal to be in the middle of its analog-to-digital converter's range. Since input
power can vary dramatically from channel to channel, day to night, and season to
season, a level adjusting system is needed.
The traditional method is to have an adjustable gain stage before the tuner and an
adjustable gain stage in the IF path. The demodulator provides an analog signal output
that adjusts the gain of the amplifiers. Analog filters are used to determine which gain
stage is adjusted. In this type of system, overall gain adjustments of 40 to 60 dB are
possible, and either the RF LNA or the IF Automatic Gain Control (AGC) amplifier
actively adjusts power. The RF input power that corresponds to the switch between the
RF Gain Control and the IF Gain Control is called the attack point. Roll your mouse
pointer over each amplifier for more information.
21
Gain in an AGC System
85
Gain (dB)
75
65
RF Gain
IF Gain
Total Gain
55
45
35
25
15
-25
-5
15
Input Signal Level (dBmV)
Here you can see a system with what's called a 0 dBmV attack point.
When the RF input power is very low, the RF front-end AGC gain is at
maximum. As the input power rises, the IF AGC gain is reduced. At 0
dBmV, the IF gain is reduced to its minimum value. Above 0 dBmV, the
IF gain is held constant while the RF gain is reduced. The choice of the
attack point is a system design issue based on the overload
characteristics of the various gain stages. This choice allows for the best
noise figure for low-level signals while maintaining good performance
with high-level signals. This approach is commonly called delayed AGC.
22
MC44C801 Silicon Tuner IC
(2)
(1)
Mouse over each numbered arrow to learn more.
(3)
BPF
50 to 861 MHz
RF In
(4)
1120 MHz First IF
1064 MHz
to 1176 MHz
Mixer
Amp
1175 to 1975 MHz
36 to 46 MHz
IF Out
Mixer
(5)
Variable Gain LNA
VCO
Loop
Filter
Charge
Pump
Divide
By A
Divide
By N
Prescaler
5/6
VCO
Divide
By N
22-Bit
Data
Register
External
Loop
Filter
Phase
Detector
Ref
Divider
100 / 200
/ 400
OSC
Charge
Pump
5V
Tracking
Regulator
3.6 V
MC44C801 Silicon Tuner IC
SClk
MOSI
SS
MISO
(6)
Divide
By A
Ref
Divider
1/2
Amp
25 MHz
Phase
Detector
Prescaler
5/6
(8)
(7)
(1) Integrated variable gain LNA with 21dB of programmable gain control (2) Up conversion mixer (3) Down conversion
mixer (4) Fully integrated first VCO and loop filter (5) Second VCO requiring only an external inductor (6) On-chip
reference oscillator (7) SPI interface bus (8) On-chip voltage regulator
Let’s look at Freescale Silicon Tuner products. Here you can see a block diagram of the Gen2
Silicon Tuner IC, part number MC44C801. This is a dual conversion tuner. In simplest terms, this
device takes in RF signals in the 50 MHz to 861 MHz range and converts them to an IF between 36
MHz and 46 MHz for output. The standard IF frequency used in North and South America as well
as South Korea is 44 MHZ to 45 MHz; 58 MHz in Japan, and 36 MHz to 39 MHz in the rest of the
world.
Roll your mouse pointer over each numbered arrow to learn more about the MC44C801’s features.
The MC44C801 is driven by an external single 5V supply and a 25-MHz crystal. The on-chip 22-bit
data register is set with predetermined system values via the serial peripheral interface (SPI)
interface bus.
RF signals in the 50 MHz to 861 MHz range are input to the device. At this point, a predetermined
amount of gain is added to the signal via the variable gain LNA. As the signal reaches the up
conversion mixer, it is mixed with input from the first LO. The signal is up converted to a frequency
in the 1120 MHz range and sent off chip to an external filter. In this example, the external filter is a
1120-MHz SAW filter. This eliminates any unwanted images, making further processing much
easier. The signal is brought back on chip to pass through the down conversion mixer with input
from the second LO. Now, the IF signal is in the 36 MHz to 46 MHz range, and it is output from the
chip for further system processing.
Using this device has significant benefits. The integration surrounding the two LOs (VCO 4 and 5)
eliminates the need for additional costly, precision components. The MC44C801 device has also
eliminated the need for high voltage (30V) and analog (9V) supplies.
Click “MC44C801” to see an enlarged view of this block diagram.
23
MC44C801
(2)
(3)
(1)
BPF
50 to 861 MHz
1120 MHz First IF
RF In
Amp
36 to 46 MHz
1064 MHz
to 1176 MHz
Mixer
(4)
1175 to 1975 MHz
IF Out
Mixer
(5)
Variable Gain LNA
VCO
Loop
Filter
Charge
Pump
25 MHz
Divide
By A
Divide
By A
Prescaler
5/6
Divide
By N
Ref
Divider
1/2
Amp
Divide
By N
22-Bit
Data
Register
VCO
External
Loop
Filter
Phase
Detector
Ref
Divider
100 / 200
/ 400
OSC
Charge
Pump
5V
Tracking
Regulator
3.6 V
MC44C801 Silicon Tuner IC
SClk
MOSI
SS
MISO
(6)
Phase
Detector
Prescaler
5/6
(8)
(7)
(1) Integrated variable gain LNA with 21dB of programmable gain control (2) Up conversion mixer (3) Down
conversion mixer (4) Fully integrated first VCO and loop filter (5) Second VCO requiring only an external
inductor (6) On-chip reference oscillator (7) SPI interface bus (8) On-chip voltage regulator
24
MC44C801 Key Performance Specs
Parameter
MC44C801
Frequency Range
50 to 861 MHz
Conversion Gain
38 dB
Gain Control Range
21 dB
Noise Figure
<6 dB
CSO
@-4 dBmV, -66 dBc
CTB
@-4 dBmV, -63 dBc
Cross-modulation
@-4 dBmV, -58 dBc
Passband Gain Flatness
+ 0.5 dB
Sideband Noise @ 10 kHz
–94 dBc/Hz
Here are some important performance specifications for you to remember
because they can demonstrate to customers how the MC44C801 can be
valuable in their implementations.
Let’s highlight some of these features. The frequency range provides
support for the majority of TV channels. The key performance figures of
the MC44C801 are its noise figure, CSO and CTB. In today's
environment, a CSO and CTB of greater than 60 dB is very good; in fact,
it is required in the majority of current tuning systems. The MC44C801
exceeds this requirement and provides the functionality and performance
specifications that customers look for when trying to solve this portion of a
system design.
25
MC44C801 Gain Control
Tuner
IF
RF Input
IF AGC
Amp
Demodulator
Analog
Voltage
Digitally
controlled LNA
Gain Control Register
SPI Bus
Processor
In the MC44C801 dual conversion silicon tuner, a digitally controlled LNA is
included in the front end. The LNA can be programmed through the SPI port
to provide between -9 dB and +12 dB of gain.
Unlike the traditional analog AGC approach, a microprocessor is involved in
the AGC process. In this system, the demodulator controls the back-end IF
AGC through the standard analog method while the processor controls the
front-end AGC. The processor is able to calculate the input power of the two
channels and then set the front-end gain appropriately. A combination of
laboratory and factory calibration makes this method work.
For a given design, each of the contributors to gain variation can be
measured and calibrated in the lab. For example, the front-end gain is known
by the set point applied to it. The tuner and IF gain can be measured and
compensated for, if necessary. IF AGC amps are usually operated in the
linear range so the processor can determine the gain of the AGC amp by
reading the demodulator’s gain control register.
The end result of all of these measurements and calibrations is that the
processor can infer the input power by knowing the LNA setting, AGC control
register value, tune frequency, and mixer settings. This technique has been
successfully used to meet DOCSIS 2.0 requirements of +/- 3 dB of accuracy
for power measurements. A version of this power management software is
delivered with the evaluation kit (EVK).
26
Question
Does this block diagram accurately represent how RF signals flow through the
MC44C801? Click Done when you are finished.
Amp
Yes
50 to 861 MHz
RF In
BPF
1120 MHz First IF
Mixer
No
1175 to 1975 MHz
Loop
Filter
VCO
Prescaler
5/6
Divide
By A
1064 MHz
to 1176 MHz
Divide
By A
Prescaler
5/6
Mixer
VCO
36 to 46 MHz
IF Out
External
Loop
Filter
Done
Here is a question to check your understanding of RF signals and the MC44C801
tuner.
Correct!
This diagram does not accurately represent the MC44C801. In the MC44C801, the
variable gain LNA is located between the RF In and the first mixer.
27
SPI Interface Bus
• Very straightforward
• Many controllers do not have hardware support for SPI because it is
so simple
• 4 GPIO lines are used to implement
• Very simple code
• Multiple tuners can share the bus, requiring 1 more GPIO for each
additional device
• Fast, 10 MHz clock
The SPI interface bus is used to communicate with the silicon tuner. All the
programming for channel changes and gain settings are done over the SPI
interface. It is so straightforward that most microprocessor controllers don't
have hardware support for them, but it's very easy to implement using just
four general-purpose input-output (GPIO) lines.
Click “SPI Code” to see the main section of code.
Multiple tuners can share the bus, requiring one more GPIO for each
additional device. The SPI interface bus is also very fast, with a 10 MHz
clock.
Some customers want an I2C bus rather than the SPI bus because that's
what they're currently using, but as you can see, the lack of an I2C should
not prevent them from using the MC44C801 because the SPI is not difficult
to implement. They don't actually have to write the code to support the SPI
bus because Freescale provides it. The application note "SPI
Implementation for the MC44C801 Silicon Tuner IC" provided in the EVK
has more information.
28
SPI Code
This is the main routine for
communication back and forth
between the processor and the
tuner, though other code is used
for initialization.
unsigned long spi_rxtx (unsigned long txword, int
len){
int cntr;
unsigned long read;
int nop;
read = 0;
txword = txword << (32 - len);
g_imm->pp.PADAT |= (SPI_CLK);
g_imm->pp.PADAT |= (SPI_SEL);
for (cntr = 0; cntr < len; cntr++) {
if (txword & 0x80000000){
g_imm->pp.PADAT &= ~(SPI_TX);}
else {
g_imm->pp.PADAT |= SPI_TX; }
read = read << 1;
for (nop = 0; nop < 1; nop++);
g_imm->pp.PADAT &= ~(SPI_CLK);
if ((g_imm->pp.PADAT & SPI_RX) == 0){
read |= 0x0001; }
for (nop = 0; nop < 1; nop++);
g_imm->pp.PADAT |= SPI_CLK;
txword = txword << 1;
}
read = read << 1;
g_imm->pp.PADAT &= ~(SPI_SEL);
return (read);
}
29
MC44S802 Silicon Tuner IC
Mouse over each numbered arrow to learn more.
1020 to 1220 MHz First IF
(1) LNA
36 or 44 MHz Second IF
BPF
LC Filter
57 - 861 MHz
From
Diplexer
(2) Fully Integrated Second IF
Mixer
Diff
Amp
Diff
Amp
LNA
Cntl A
Cntl B
Diff
Amp
Mix 1
Pre Amp 1
Mixer
Diff
Amp
Post Amp 1
Diff
Amp
Pre Amp 2
VCO
Mix 2
Mixer
1077 to 2081 MHz
External
Loop
Filter
Multiple Output (3)
Paths
BPF
LPF
IF AGC Amp
Diff
Amp
Post Amp 2
Diff
Amp
IF Amp
VCO
976 to 1184 MHz Quadrature
External
Loop
Filter
1952 to 2368 MHz
Charge
Pump 1
Phase
Detector 1
Divide
By N1
AGC Control
To Analog
Demod
VCO
Generator
Div by 2
VCO
To Digital
Demod
Divide
By N2
Phase
Detector 2
Charge
Pump 2
Shut Dn
3.3 V
(4)
Multiple
Output
Paths
Gain Select
250 / 125 / 62.5 kHz
Osc
Buffer
Amp
LPF
Divide
By R3
Divide
By R1
Divide
By R2
Data Register
Clock
Freescale CMOS Silicon Tuner IC
3.3V
power
supply
BusSelect
MOSI / SDA
SPI/I2C Bus
Interface (6)
SS /Addr 1
4 to 28 MHz
Crystals
SPI / I2C BUS
Interface
Digital
AGC
MISO / Addr 2
(5)
(7)
1.8V
Regulator
OSC
4 to 28 MHz
3.0V
Regulator
Here you can see a block diagram of the Gen3 Silicon Tuner IC, part number MC44S802. This is a
dual conversion Silicon Tuner with integrated IF AGC amp. The MC44S802 builds off of the
MC44C801 functionality with several enhancements.
Roll your mouse pointer over each numbered arrow to see some of these enhancements.
With regard to front-end improvements, the LNA has been improved with reduced gain roll-off. The
gain control range has been modified to support either 40 dB or 60 dB of gain control. Users can
implement analog or digital gain control, and they can also switch between these two AGC control
systems for use in dual-demodulator systems.
The fully integrated second IF provides multiple output paths for the down converted IF signal,
again for the benefit of dual demodulator systems. The two paths provided are via an IF AGC amp
to the digital demodulator and via an IF amp to the analog demodulator. The benefit of this
integrated feature is that it enables customers to develop more cost-effective systems. With the
addition of this feature, users don't have to provide this functionality off chip and thus add expense
to their overall bill of material.
Another enhancement is that customers can program the device via an I2C interface bus as well as
the SPI interface.
Finally, the MC44S802 can be implemented with crystals that range from 4 MHz to 28 MHz, and it
works off of a single 3.3V power supply.
The biggest benefit to users of the MC44S802 is that its power consumption has been reduced
significantly from the previous MC44C801 product. The MC44S802 consumes approximately
800mW of power , and implementing an external IF amp can further reduce power use to about
500mW.
Click “MC44S802” to see an enlarged view of this block diagram.
30
MC44S802
1020 to 1220 MHz First IF
(1) LNA
57 - 861 MHz
From
Diplexer
(2) Fully Integrated Second IF
36 or 44 MHz Second IF
BPF
LC Filter
Mixer
Diff
Amp
Diff
Amp
LNA
Diff
Amp
Mix 1
Pre Amp 1
Cntl A
Cntl B
Mixer
Diff
Amp
Post Amp 1
Diff
Amp
Pre Amp 2
VCO
Mix 2
Mixer
1077 to 2081 MHz
External
Loop
Filter
Multiple Output (3)
Paths
BPF
IF AGC Amp
Diff
LPF Amp
Post Amp 2
Diff
Amp
IF Amp
VCO
976 to 1184 MHz Quadrature
External
Loop
Filter
1952 to 2368 MHz
Charge
Pump 1
Phase
Detector 1
Divide
By N1
AGC Control
To Analog
Demod
VCO
Generator
Div by 2
VCO
To Digital
Demod
Divide
By N2
Phase
Detector 2
Charge
Pump 2
Shut Dn
3.3 V
(4)
Multiple
Output
Paths
Gain Select
250 / 125 / 62.5 kHz
Osc
Buffer
Amp
LPF
Divide
By R3
Divide
By R1
Divide
By R2
Data Register
Clock
BusSelect
MOSI / SDA
SPI/I2C Bus
Interface (6)
SS /Addr 1
4 to 28 MHz
Crystals
SPI / I2C BUS
Interface
Digital
AGC
MISO / Addr 2
(5)
(7)
1.8V
Regulator
OSC
4 to 28 MHz
3.0V
Regulator
Freescale CMOS Silicon Tuner IC
3.3V
power
supply
Motorola Confidential Proprietary
31
Silicon Tuners vs. CAN Tuners
MC44C801
CAN Tuner
Silicon tuner benefits:
• No tracking filters, thus no manual
tuning
• Improved temperature response
• Improved aging performance
• Lower manufacturing costs
• Can be integrated on main board
• Lower cost
Here you can see the MC44C801 as implemented on a reference card and
a CAN tuner. The silicon tuner, which is a dual conversion tuner, has many
benefits over a CAN tuner. No tracking filters are required, so no manual
tuning needs to be done. Silicon tuners have improved temperature
response as well as improved aging performance.
Operating the device within temperature and over time, has no impact on a
silicon tuner compared to a CAN tuner, which will suffer from both of these
conditions.
The silicon tuner can be integrated on the customer's main board, whereas
you can see from the lower right-hand picture of the implementation of the
CAN tuner, it's implemented as sort of a daughtercard, perpendicular to the
PCB plane itself. Implementing a silicon tuner IC instead of a CAN tuner will
ultimately lower the cost of implementation, not only from the components
perspective but from the reduced manufacturing manpower.
32
Question
What are some of the enhancements of the MC44S802 compared to the
MC44C801? Select all that apply and then click Done.
Significantly smaller footprint
Second IF provides multiple output paths for the down converted IF signal
Faster signal conversion
Customers can program the device via an I2C interface bus as well as the SPI interface
Greatly reduced power consumption
Done
Please select all the statements that describe the enhanced features of the
MC44S802 compared to the MC44C801.
Correct.
The MC44S802 has a second IF that provides multiple output paths for the
down converted IF signal, customers can program the device via an I2C
interface bus as well as the SPI interface, and greatly reduce power
consumption. These features are all enhancements not available on the
MC44C801.
33
Course Summary
•
•
•
•
•
•
•
CAN tuners (single conversion)
Silicon tuners (dual conversion)
Advantages of using silicon tuners
Applications for silicon tuners
Single conversion and dual conversion tuners
MC44C801 Silicon Tuner IC
MC44S802 Silicon Tuner IC
In this course, you learned that tuners receive audio/video programming via an
RF broadcast, then select and convert a single signal into a lower, more
workable frequency. Silicon tuners are highly integrated circuits that provide
this functionality in a single chip as opposed to the short-lived, more expensive
CAN tuners. Silicon tuners can be used in Cable modems, CATV set-top
boxes (analog and digital), CATV Media Gateway, and Computer TV tuner
cards (analog and digital). You also learned about the advantages of dual
conversion tuners, which don’t use tracking filters like single conversion tuners.
Finally you learned about the MC44C801 and MC44S802 tuners, which have
lower costs, lower power consumption, and superior performance in areas
such as CSO and CTB as compared to the competition.
34
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